In this world of high-speed connectivity and wireless communication, the importance of electromagnetic compatibility (EMC) has reached a new high in history. EMC is particularly important for the application of battery electric vehicles, as its power transmission system generates extremely high transient voltages (dV/dt).

The basic concepts of electromagnetic interference (EMI) (problem) and electromagnetic compatibility (solution) are evident in all applications. Having a deep understanding of EMI and EMC is an important topic for any automotive engineering team. The significant increase in vehicle network architecture and wireless connectivity reveals the potential impact of unnecessary noise on vehicle applications.

Electromagnetic fields are ubiquitous, and whenever high-frequency currents that change over time flow through wires or printed circuit traces, magnetic flux lines (H field) and electric fields (E field) will surround the conductive medium. When transmitted to another PCB trace or cable, these electromagnetic fields will appear as unwanted signals or noise, thus interfering with the operation of the circuit.

Electrostatic discharge (ESD) is another form of EMI that we encounter when getting off the car or performing any action that may cause friction. The occurrence of ESD is irregular, while EMI usually occurs continuously. Any high voltage, short duration (high dV/dt) transient can lead to unstable operation and even permanent damage to sensitive electronic systems.

Any complex electronic circuit has multiple potential sources of EMI, including clocks, analog signal input lines, relay switches, microcontroller interfaces, and DC/DC converters. EMI may cause problems in the systems it generates and other completely unrelated systems. EMI may occur regularly or occasionally, so identifying the source of EMI can be quite time-consuming and requires testing equipment such as a spectrum analyzer.

EMI can be transmitted to another system through two main channels: conduction radiation or radiation radiation. Radiation radiation typically comes from signals operated at radio frequencies, such as microcontroller data lines, clocks, and wireless transceivers. PCB traces and interconnects above 30 MHz become extremely effective antennas.

Conducted radiation may be generated by inductance, capacitance, or common impedance coupling, and noise artifacts can interfere with other systems or functions. The crosstalk generated by inductive or capacitive coupling between signal lines is another term used to describe EMI. Common impedance coupling typically occurs on the power rail, where small voltage fluctuations related to a particular circuit function and load are superimposed on the power line shared with other system components. Automotive engineers understand the potential impact of electromagnetic radiation generated inside electric vehicles

Types of electromagnetic radiation

EMI diagram

This figure shows the transmission of electromagnetic noise from the source to the receiving (interrupt) system or circuit functions that are not required.

The rise of connected vehicles

Modern vehicles are equipped with various interconnected electronic systems, stylish infotainment displays, and advanced driving assistance systems (ADAS), making our road trips safer. However, there are many potential sources of EMI and susceptible systems in vehicles, especially electric vehicles (EVs), whose high power conversion and transmission system functions may cause serious electronic interference, which in turn affects other electronic control units (ECUs).

Electric vehicles have amazing fast dynamic response speed, some of which can accelerate from 0 miles per hour to 60 miles per hour in 5 seconds. During the acceleration process, the electrical load generated through the transmission system and related circuits can reach up to 1000 amperes and generate tens of thousands of volts of instantaneous dV/dt transients. Compared to low voltage signals from steering wheel rotation sensors used for ADAS lane guidance, if any transmission system transient interferes with the ADAS ECU, the integrity of the lane guidance function will be severely compromised.

The architecture of modern vehicles is increasingly shifting towards regional, using high-speed networks to connect regions and related ECUs.

Regional Architecture in Modern Vehicles

Electrical system diagram

Modern vehicles use a regional network architecture to connect electronic control units.

(Data source: Anfuli)

In addition, the addition of wireless connections such as passenger information entertainment systems, vehicle to vehicle infrastructure (V2X), and vehicle to vehicle (V2V) communication has also added the possibility of EMI. With so many interconnected systems equipped with electrically sensitive processors and long network wiring, it is more likely to generate EMI artifacts, disrupt and damage vehicle operations.

Realize electromagnetic compatibility

The EMC of electric vehicles has two key points. The first is to ensure that circuits that can generate any form of EMI do not conduct or emit interference, and the second is to protect systems susceptible to EMI.

The unknown is that vehicles, drivers, and passengers may encounter many different situations even during short journeys. For example, when passengers operate a touch device to turn it into an antenna and emit unnecessary signals, it increases the EMI of the entertainment display and affects other systems.

EMI immunity has become an important area of vehicle testing, and for most countries/regions around the world, compliance with standards such as EU ECE R10, CISPR 25, or ISO 11451/2 is crucial. These standards cover specifications for EMC sensitivity to both internal and external sources of vehicles, and similarly, external radiation of vehicles also needs to be regulated.

For automotive electronics engineers, there are multiple established methods to achieve EMC compliance.

Analyze and investigate EMI hotspots: Spectrum analyzers equipped with H-field and E-field probes and professional EMI receivers can identify noise sources from PCB traces and active devices such as switching transistors, microcontrollers, and wireless modules. In addition, there are valuable resources such as circuit modeling and simulation techniques, which can be simulated using professional software for radiation and sensitivity.

Implementing EMI countermeasures: After reducing noise artifacts to specific components or functions, available EMI suppression measures include grounding planes, metal masks, passive filters, ferrite cores, and mask interconnections. For some RF sensitive and high-power applications, metal gaskets and masks are necessary. Similarly, circuits that are susceptible to EMI should also be protected. The differential signal method is widely used in many automotive network applications due to its inherent EMI anti-interference ability; However, maintaining signal integrity is also crucial.

Spectral analyzer with near-field probe for measuring EMI

Schematic

A spectrum analyzer containing a near-field probe measures the EMI of the microcontroller board. (Data source: Robert Huntley)

PCB design and mechanical casing: Careful PCB design is extremely important for EMC, and professionally planned PCB configurations and resources are available for engineers to follow. Using metal casings, mask interconnections, and decoupled power rails as much as possible can greatly help achieve compliance with necessary standards.

Realize electromagnetic compatibility of electric vehicles

There is no shortcut to meeting internationally recognized EMC standards, and the path to success begins with detailed engineering design decisions and a thorough understanding of basic technology. This article introduces the basic concepts of EMI, ESD, and EMC, as well as some preliminary checklist items.